An ArrayList is a resizable array implementation of the List interface in Java. It allows you to store a collection of elements, which can be accessed and modified easily. Unlike regular arrays, an ArrayList can grow or shrink in size as needed, making it more flexible for managing dynamic data. ArrayLists are part of the Java Collections Framework and provide various methods for adding, removing, and searching for elements. They maintain the order of insertion, meaning that elements can be accessed by their index. This makes ArrayLists a popular choice for many programming tasks that require a list-like structure.